1. Field of the Invention
The invention relates to a novel process for the preparation of bicyclic amidines by reaction of lactones with primary amines. The invention also relates to novel bicyclic amidines having functional groups, especially amino, hydroxyl and/or mercapto groups, and to their use as catalysts for the preparation of polyurethanes.
2. Background Art
Bicyclic amidines are strong organic bases which, owing to their high basicity coupled with low nucleophilicity and their ready solubility in almost all solvents, have found numerous applications. Particularly well-known bicyclic amidine compounds are those commonly referred to by the abbreviations DBN and DBU, i.e., 1,5-diazabicyclo[4.3.0]non-5-ene (2,3,4,6,7,8-hexahydropyrrolo[1,2-a]pyrimidine) and 1,8-diazabicyclo[5.4.0] undec-7-ene(2,3,4,6,7,8,9,10-octahydropyrimido[1,2-a]azepine), respectively.
A review of the uses of these compounds in chemical syntheses can be found, for example, in Synthetica Merck, Volume II, E. Merck, Darmstadt, (1974), pp. 118-119 and 124.
A known process for preparing bicyclic amidines starts from N-(xcfx89-aminoalkyl)lactones which, when heated with acidic catalysts, undergo cyclization with elimination of water to form the amidines (German Patent No. C 1,545,855). The N-(xcfx89-aminoalkyl)lactones are obtained, for example, from the corresponding cyano compounds by hydrogenation; in particular, for example, N-(xcex3-aminopropyl)pyrrolidone is obtained from N-(xcex2-cyanoethyl)-pyrrolidone [see, e.g., W. Reppe et al., Justus Liebigs Ann. Chem., 596, (1955), p.211]. It is also possible to prepare N-(xcfx89-aminoalkyl)lactones from the corresponding lactones and xcex1,xcfx89-diaminoalkanes (German Patent No. C 730,182). The known processes for the preparation of bicyclic amidines have the disadvantage that they include at least two synthesis steps with working up of the intermediates.
It is known that bicyclic amidines are highly suitable as catalysts for the preparation of polyurethanes (French Patent No. 1,542,058). A considerable disadvantage of this use, however, is that bicyclic amidines are not firmly bonded within the polyurethane formed and therefore, over time, diffuse out of or are extracted from the polyurethane. In each case there is unnecessary pollution of the environment.
The main object of the invention is to provide an improved and simplified process for the preparation of bicyclic amidines and, from this class of compounds, to provide new compounds which, when used as catalyst for the preparation of polyurethanes, are bonded so firmly to the polymer that they no longer have any notable tendency towards migration. Other objects and advantages of the invention are set out herein or obvious to one skilled in the art.
The objects and advantages of the invention are achieved by the preparation process of the invention, the novel compounds of the invention and the process of using the novel invention compounds.
The invention preparation process involves preparing bicyclic amidines of the general formula: 
wherein A and B are defined below, in a one-pot process, without isolation or purification of intermediates, from the corresponding lactones of the general formula: 
wherein A is defined below, and amines of the general formula:
H2Nxe2x80x94Bxe2x80x94NH2xe2x80x83xe2x80x83III 
wherein B is defined below.
The group A in the lactone (II) and in the amidine (I) is in each case a 3-, 4- or 5-membered carbon chain of the formula xe2x80x94CR1R2xe2x80x94CR3R4xe2x80x94CR5R6xe2x80x94, xe2x80x94CR1R2xe2x80x94CR3R4xe2x80x94CR5R6xe2x80x94CR7R8xe2x80x94 or xe2x80x94CR1R2xe2x80x94CR3R4xe2x80x94CR5R6xe2x80x94CR7R8xe2x80x94CR9R10xe2x80x94, where R1 and R2 are in each case attached to the carbon atom which is adjacent to the heteratom.
The group B in the amine (III) and in the amidine (I) is in each case a 2-, 3- or 4-membered carbon chain of the formula xe2x80x94CR11R12xe2x80x94CR13R14xe2x80x94, xe2x80x94CR11R12xe2x80x94CR15R16xe2x80x94CR13R14xe2x80x94 or xe2x80x94CR11R12xe2x80x94CR15R16xe2x80x94CR17R18xe2x80x94CR13R14xe2x80x94.
The general formula I, therefore, encompasses bicyclic amidines having 5-, 6- or 7-membered rings; the two rings can have identical or different numbers of members. Correspondingly, the general formula II encompasses lactones having from 5 to 7 ring members, in other words, xcex3-, xcex4- and xcex5-lactones.
The substituents R1, R2, and R11 to R14 of the carbon chains A and B are, in each case independently of one another, hydrogen, C1-C4-alkyl or aryl or C1-C4-alkyl groups which are in turn substituted with hydroxyl, amino, C1-C4-alkylamino or mercapto. The substituents R3 to R10 and R15 to R18 can be either the groups mentioned for R1, R2 and R11 to R14 or else hydroxyl, amino, C1-C4-alkylamino or mercapto groups.
C1-C4-alkyl here refers to all primary, secondary and tertiary, unbranched or branched alkyl groups having up to 4 carbon atoms, for example, methyl, ethyl, propyl, butyl, isopropyl, isobutyl, sec-butyl, and tert-butyl. Aryl refers in particular to phenyl or to alkyl-substituted phenyl, such as, o-, m- or p-tolyl or the various isomeric xylyl groups. Examples of suitable lactones are xcex3-butyrolactone, xcex3- and xcex4-valerolactone, xcex5-caprolactone or substituted lactones such as pantolactone (2-hydroxy-3,3-dimethyl-xcex3-butyrolactone).
Functional groups as substituents, that is, hydroxyl, amino, alkylamino or mercapto, are preferably located on the groups B of the amine component (III).
Amines (III) which are suitable are therefore not only primary diamines but also compounds having additional primary or secondary amino groups. Examples of suitable amines are 1,2-diaminoethane, 1,2-diaminopropane, 1,3-diaminopropane, 1,2,3-triaminopropane, 1,1,1-tris(aminomethyl)ethane or tetrakis (aminomethyl)-methane. If amines having non-equivalent amino groups are employed, then under some circumstances mixtures of products can be formedxe2x80x94as in the case, for example, with 1,2-diaminopropane or 1,2,3-triaminopropane.
When reacting the lactone (II) with the amine (III) it is advantageous to use a molar ratio of at least 1 mol of amine to 1 mol of lactone (i.e., 1 to 30 mols per mol). Preferably, from 2 to 20 mols of amine are employed per mole of lactone. The excess of amine can be recovered when working up the reaction mixture.
The reaction is advantageously carried out at a temperature of at least 150xc2x0 C. The reaction temperature is preferably between 200xc2x0 and 300xc2x0 C. The addition of an inert solvent, such as, toluene or xylene, while possible, is not necessary. The reaction is preferably carried out without solvent. In order to attain the reaction temperature it is generally necessary to maintain the reaction mixture under elevated pressure, since the boiling points of many starting materials at atmospheric pressure are lower than the reaction temperature. In order to achieve this, customary autoclaves can be employed. In order to accelerate the reaction it is preferable to add an acidic catalyst. Suitable catalysts are Brxc3x8nsted acids, such as, hydrochloric acid, sulfuric acid, phosphoric acid or ammonium chloride, or alternatively acidic aluminium silicates or acidic metal oxides, such as, tin (IV) oxide or antimony (III) oxide.
In accordance with the invention, the reaction mixture is distilled directly without isolating an intermediate. For practical reasons, this is typically carried out by transferring the reaction mixture from the autoclave to a distillation apparatus. If appropriately equipped apparatus suitable both for superatmospheric pressure and reduced pressure is available, the reaction of the lactone with the amine and the distillation can be carried out in one and the same apparatus. In the distillation, the initial fraction passing over is the water formed during cyclization and the excess amine, followed by the amidine. Depending on the boiling point of the product, the distillation is carried out at an appropriately reduced pressure.
Using the process according to the invention, the known bicyclic amidines mentioned in the background section, such as, DBN and DBU, but also, in particular, novel compounds from this class of substances, having previously unobtained properties, can be prepared.
It has been found that those bicyclic amidines (I) in which at least one of the substituents R1 to R18 is and/or carries a primary or secondary amino group, a hydroxyl group and/or a mercapto group can be used as catalyst for the preparation of polyurethanes and are bonded so firmly within the polymer that no migration can be detected either during use or in the course of the customary extraction tests. It is presumed that, during the preparation of the polyurethane, these additional functional groups react with the isocyanate groups of the isocyanate component of the polyurethane and form covalent bonds.
The additional functional groups can of course also be used for other organic reactions with polymeric or nonpolymeric isocyanates, epoxides, carboxylic acids, carboxylic acid derivatives or other compounds.
The additional functional groups are preferably amino groups or aminoalkyl groups, such as, aminomethyl groups. They are preferably located on the chain which in the general formula is designated xe2x80x9cBxe2x80x9d, in other words in the positions of substituents R11 to R18.
The compounds which are particularly preferred are 3-amino-2,3,4,6,7,8-hexahydropyrrolo[1,2-a]pyrimidine: 
3-(aminomethyl)-2,5,6,7-tetrahydro-3H-pyrrolo[1,2-a]imidazole: 
both individually and as a mixture,
and 3-(aminomethyl)-3-methyl-2,3,4,6,7,8-hexahydropyrrolo [1,2-a]pyrimidine: 